Conveyor systems comprising a number of rollers disposed parallel to one another and connected to one another by belts are used widely in industry to convey goods. Some of the rollers in the conveyor system, so-called drive rollers, contain an electric motor as part of a roller drive, with the aid of which a rotational movement of the drive roller is generated.
The roller drive generally comprises a hollow rotor with permanent magnets, in which a fixed stator made from an iron core and having a number of windings is disposed. For its part the rotor is connected to an external roller tube of the drive roller, so that the roller tube is rotated with the rotor during operation of the roller drive.
During operation the electrical power loss of the roller drive generates heat, which heats the roller tube by way of which the goods are transported. The heat is emitted to the surroundings and thus to the goods transported by means of the conveyor system by way of the roller tube. To prevent damage to the goods, only a limited increase in the temperature of the roller tube is permitted, for example from approximately 40 to 50 Kelvin.
The roller drive is generally positioned in the center of the drive roller and its length is approximately 25% to 50% of the length of the roller tube. This produces an irregular temperature distribution on the roller tube surface. In the region of the heated roller drive the roller tube assumes a significantly higher temperature than in the outer regions away from the roller drive, since the thermal conduction of the roller tube, which is made of steel, is poor. The roller tube cannot be made from a material with better thermal conduction properties, such as aluminum or copper for example, as it is used for the magnetic shunt for the flux of the permanent magnets of the rotor and therefore has to be made from a magnetizable material, such as steel for example.
There are currently measures for eliminating some of the heat generated in the roller drive, for example by way of a heat tube or heat pipe, which is filled with a heat transfer medium. However such a heat pipe requires a greater shaft diameter in the motor shaft so the diameter of the stator has to be reduced. This leaves less space for the iron core or for the windings, resulting in a reduction in torque.